Natural hybridization between two butterfly bushes in Tibet: dominance of F1 hybrids promotes strong reproductive isolation

BackgroundIt has been recognized that a certain amount of habitat disturbance is a facilitating factor for the occurrence of natural hybridization, yet to date we are unaware of any studies exploring hybridization and reproductive barriers in those plants preferentially occupying disturbed habitats.Buddlejaplants (also called butterfly bush) generally do grow in disturbed habitats, and several species with hybrid origin have been proposed, based solely on morphological evidence.ResultsIn the present study, we test the hypothesis thatB. × wardiiis of natural hybridization origin in two sympatric populations of three taxa includingB. × wardiiand its parents (B. alternifoliaandB. crispa) plus 4 referenced parental populations, using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sitesB. × wardiiis likely to be a hybrid betweenB. alternifoliaandB. crispa, and moreover, we confirm that most of the hybrids examined are F1s. That these plants are F1s is further supported by morphology, as no transgressive characters were detected.B. crispawas found to be the maternal parent in the Bahe (BH) population, from cpDNA evidence. However, in the Taji (TJ) population, the direction of hybridization was difficult to establish due to the shared cpDNA haplotypes betweenB. alternifoliaandB. crispa, however we still predicted a similar unidirectional hybridization pattern due to results from cross-specific pollination treatments which supported the “SI × SC rule”.ConclusionsThe presence of mainly F1hybrids can successfully impede gene flow and thus maintain species boundaries in parental species in a typical distribution ofBuddleja, i.e. in disturbed habitats.

Natural hybridization between two butterfly bushes in Tibet: dominance of F1 hybrids promotes strong reproductive isolation

Background: It has been recognized that certain amount of habitat disturbance is a prerequisite for occurrence of natural hybridization, yet we are currently still not aware of any studies exploring hybridization and reproductive barriers to those plants preferably occupying disturbed habitats. Buddleja plants (also called butterfly bush) generally grow in disturbed habitat, and several species with hybrid origin only on basis of morphology evidence have been proposed. Results: In the present study, we test the natural hybridization origin hypothesis of B. × wardii in two sympatric populations of three taxa including B. × wardii and its parents (B. alternifolia and B. crispa) plus 4 referenced parental populations, using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sites B. × wardii was likely to be hybrids between B. alternifolia and B. crispa, and moreover, most of the hybrids examined were confirmed to be F1s. This was further supported by morphology as no transgressive characters were detected. B. crispa was found to be the maternal parent in Bahe (BH) population from the cpDNA. While in the Taji (TJ) population was difficult to distinguish the hybridization direction due to the shared haplotypes of cpDNA between B. alternifolia and B. crispa, we still predicted the similar unidirectional hybridization pattern due to results from cross-specific pollination treatments which supported the “SI x SC rule”. Conclusions: Hybrids mainly consisting of F1s can successfully impede gene flow and thus maintain species boundaries of parental species in its typical distribution of Buddleja, i.e. disturbed habitats.

Hybridization and Cutting of Buddleja Genus

Buddleia davidii, also known as butterfly bush, is a unique species in China, with extensive cultivation and promotion values. The purpose of cross-breeding is to promote environmental adaptation and improve its economic benefits as a garden plant.. As Buddleja is asexual, cutting can aid in mass production of the hybrid offspring, thus stabilising local ecosystem.

Substrate pH and Butterfly Bush Response to Dolomitic Lime or Steel Slag Amendment

Steel slag (SS) is a fertilizer amendment with a high concentration of calcium oxide, and thus capable of raising substrate pH similar to dolomitic lime (DL). Steel slag, however, contains higher concentrations of some nutrients, such as iron, manganese, and silicon, compared to DL. The objective of this research was to determine the effect of SS rate on pH in a substrate composed of 80 pine bark:20 sphagnum peatmoss (v:v), as well as growth and nutrient concentration of butterfly bush (Buddleja davidii ‘Pink Delight’ Franch.). The base substrate was amended with either DL or SS at rates of 0, 0.6, 2.4, 4.8, 9.5, or 14.3 kg·m−3. Substrates were placed into 12-L nursery containers and potted with a single butterfly bush per container. Dolomitic lime amendment resulted in higher substrate pH at rates from 0.6 to 4.8 kg·m−3 while the SS amendment caused a greater increase in pH at rates higher than 4.8 kg·m−3. Butterfly bush responded well to all but the highest SS rate applied. As the rate of SS increased to 14.3 kg·m−3, decreased Mg availability may have reduced shoot growth. Based on the results of this experiment, SS could be used as an alternative to DL. However, incorporation rates would need to be adjusted slightly higher for SS compared to DL to achieve a desired pH in the range of 6 to 6.5.

Screening Potential New Tropical Ornamentals for Alkalinity, Salinity, and Irradiance Tolerances

With the rapid introduction of new herbaceous or woody perennial tropical and subtropical taxa to the U.S. nursery trade for use as summer annuals, methods for quickly assessing their tolerances to various environmental stresses will be needed. Three screening methods, one each for substrate alkalinity, soil salinity, and varied irradiance levels, were tested on four tropical taxa, Rotheca myricoides (Hochst.) Steane & Mabb. (blue butterfly bush), Graptophyllum pictum (L.) Griff, (caricature plant), Jatropha integerrima Jacq. (firecracker jatropha), and Chrysothemis pulchella (Don. ex J. Sims) Desc. (dozakie), with potential for use as summer annuals. Specialized portable structures for testing irradiance levels were developed which minimized confounding of restricted air movement often associated with imposing shade treatments. Irradiance and salinity screening procedures were deemed successful, while further refinement is needed with the alkalinity screening method tested. Decreased irradiance levels suppressed flowering of R. myricoides, while full sun exposure decreased foliar appearance and growth of C. pulchella. Only J. integerrima showed adverse responses to elevated substrate alkalinity. Jatropha integerrima and G. pictum exhibited adaptation to a wide range of light exposures and salinity levels while maintaining attractive foliage. Although flowering of J. integerrima was reduced with heavy shade (66%), some flowering continued.

Control of Butterfly Bush with Postemergence Herbicides

Butterfly bush (Buddleja davidii) is classified as invasive in several parts of the United States. Two experiments were conducted to evaluate the effectiveness of four herbicides and two application methods on postemergence butterfly bush control. The four herbicides included: Roundup (glyphosate), Aquamaster (glyphosate), Garlon (triclopyr), and Arsenal (imazapyr). Application methods included spraying foliage with a CO2 backpack sprayer, and applying herbicide concentrate to recently cut stems (cut-stump method). Plants were treated in September with the maximum labeled rate for each herbicide. Cut-stump rates were determined such that the same amount of active ingredient was applied as in the spray treatments. Applications were made to plants several months after planting to simulate control of small recently germinated plants, and again to plants over 1 year old to simulate control of larger and more established plants. Summarizing results over both plant sizes and from two repetitions of the experiment, Roundup and Aquamaster provided higher levels of control compared to Garlon and Arsenal early in the experiment. Cut-stump applications provided more rapid control than spray applications. Despite differences in control when evaluated several weeks after application, all treated plants were dead when evaluated the following spring.